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International
Tables for Crystallography Volume F Crystallography of biological macromolecules Edited by M. G. Rossmann and E. Arnold © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. F. ch. 4.1, p. 91
Section 4.1.5.3. Techniques for evaluating crystal perfection
a
Unité Propre de Recherche du CNRS, Institut de Biologie Moléculaire et Cellulaire, 15 rue René Descartes, F-67084 Strasbourg CEDEX, France, and bDepartment of Molecular Biology & Biochemistry, University of California at Irvine, Irvine, CA 92717, USA |
The ultimate objective of structural biologists is to analyse crystals of high perfection, in other words, with a minimum of disorder and internal stress. The average disorder of the molecules in the lattice is expressed in the resolution limit of diffraction. Wilson plots provide good illustrations of the diffraction quality for protein crystals. Other sources of disorders, such as dislocations and related defects, as well as the mosaic structure of the crystal, may strongly influence the quality of the diffraction data. They are responsible for increases in the diffuse background scatter and a broadening of diffraction intensities. These defects are difficult to monitor with precision, and dedicated techniques and instruments are required for accurate analysis (reviewed by Chayen et al., 1996![[link]](/graphics/greenarr.gif)
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Mosaicity can be defined experimentally by X-ray rocking-width measurements. An overall diagnostic of crystal quality can be obtained by X-ray diffraction topography. Both techniques have been refined with lysozyme as a test case and are being used for comparative analysis of crystals grown under different conditions, both on earth and in microgravity. For lysozyme and thaumatin, improvement of the mosaicity, as revealed by decreased rocking widths measured with synchrotron radiation, was observed for microgravity-grown crystals (Snell et al., 1995; Ng, Lorber et al., 1997).
Illustration of mosaic-block character in a lysozyme crystal was provided by X-ray topography (Fourme et al., 1995). Comparison of earth and microgravity-grown lysozyme crystals showed a high density of defects in the earth-grown control crystals, while in the microgravity-grown crystals several discrete regions were visible (Stojanoff et al., 1996). X-ray topographs have also been used to compare the orthorhombic and tetragonal forms of lysozyme crystals (Izumi et al., 1996), to monitor temperature-controlled growth of tetragonal lysozyme crystals (Stojanoff et al., 1997), to study the effects of solution variations during growth on the perfection of lysozyme crystals (Dobrianov et al., 1998), and to quantify local misalignments in lysozyme crystal lattices (Otalora et al., 1999).
References
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